Many industrial liquid supply systems employ positive displacement pumps having a suction stroke during which liquid is drawn from a reservoir into the inlet of the pump. On the return stroke, no liquid flow occurs into the pump inlet. For example, pneumatically powered, positive displacement pumps are utilized in conjunction with polyester resin application equipment to supply a relatively low viscosity liquid catalyst from a catalyst supply bottle to a location where the catalyst is mixed with the polyester resin, for example, in a resin spray head. Normally, the inlet to the pump is coupled to a conduit which in turn is inserted through the top opening in the catalyst supply bottle. The conduit inlet is positioned below the liquid level in the bottle, and preferably adjacent the bottom of the bottle. For example, the liquid level in the bottle may or may not be elevated above the location of the pump inlet. Thus, the conduit forms a siphon extending from the liquid in the bottle to the pump inlet. Resin catalysts such as methyl ethyl ketone peroxide do generate small amounts of gas during storage and use. During use, this gas accumulates in the low pressure area or upper reach of the siphon to form a bubble. The bubble has been advantageously used in the past to indicate that the positive displacement pump is in fact operating as intended. During the suction stroke of the pump, the bubble in the conduit is displaced from the uppermost reach of the siphon toward the inlet of the pump. During the pump return stroke, the bubble returns to the uppermost reach of the siphon. By visually monitoring the bubble movement, an indication of pump operability is obtained.
As the pump continues to operate, drawing liquid from the supply bottle, the bubble in the supply tube tends to grow because gases are generated by the liquid catalyst. If the pump operator does not carefully monitor the bubble growth, the bubble can grow sufficiently large so that the siphon from the supply bottle to the pump inlet is broken, allowing air to be drawn into the pneumatically powered pump. If air is drawn into the pump, the catalyst pump cavitates and will not pump the liquid catalyst until the operator reprimes the pump. In hot summer weather, the siphon may break several times a day, which can cause defective plastic parts due to lack of catalyst.
Accordingly, it is a broad object of the present invention to provide a fluid coupling between the liquid supply bottle and the pump inlet that eliminates the siphon effect normally encountered. It is a further object of the present invention to provide a fluid coupling that provides a visual indication of pump operation.